login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A144521 Tetrahedral numbers composed of one prime and two nonprimes. 0
0, 20, 56, 84, 165, 220, 364, 455, 680, 816, 1140, 1330, 1771, 2024, 2300, 3654, 4060, 4960, 5456, 7770, 8436, 9139, 10660, 11480, 13244, 14190, 16215, 17296, 18424, 23426, 24804, 26235, 32509, 34220, 37820, 39711, 47905, 50116, 52394, 57155 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..40.

EXAMPLE

If n-1=0(nonprime), n=1(nonprime) and n+1=2(prime), then 0*1*2/6=0=a(1). If n+3=4(nonprime), n+4=5(prime) and n+5=6(nonprime), then 4*5*6/6=20=a(2). If n+5=6(nonprime), n+6=7(prime) and n+7=8(nonprime), then 6*7*8/6=56=a(3). If n+6=7(prime), n+7=8(nonprime) and n+8=9(nonprime), then 7*8*9/6=84=a(4). If n+8=9(nonprime), n+9=10(nonprime) and n+10=11(prime), then 9*10*11/6=165=a(5). If n+9=10(nonprime), n+10=11(prime) and n+11=12(nonprime), then 10*11*12/6=220=a(6). If n+11=12(nonprime), n+12=13(prime) and n+13=14(nonprime), then 12*13*14/6=364=a(7), etc.

MAPLE

isPr := proc(n) if isprime(n) then 1; else 0; end if; end proc: for n from 0 to 300 do if isPr(n)+isPr(n+1)+isPr(n+2) = 1 then printf("%d, ", n*(n+1)*(n+2)/6 ) ; end if; end do: [From R. J. Mathar, May 01 2010]

CROSSREFS

Cf. A000040, A000392, A141468, A152622.

Sequence in context: A059677 A108108 A123456 * A044122 A044503 A109806

Adjacent sequences:  A144518 A144519 A144520 * A144522 A144523 A144524

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Dec 15 2008

EXTENSIONS

Corrected (455, 14190, 17296 inserted, 16560 removed etc.) by R. J. Mathar, May 01 2010

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified June 28 09:49 EDT 2017. Contains 288813 sequences.